U.S. Pat. No. 3,411,168 is an example of a mechanically-operated, vertically-storing dock leveler. The illustrated dock leveler includes a spring counterbalance to assist in operation. The spring counterbalance mechanism includes a spring, a roller, a cam and an arm. The spring counterbalance tends to urge the dock leveler into the stored, vertical position. During operation, as the dock leveler rotates toward an operative position, the weight moment of the dock leveler overcomes the upward bias of the spring counterbalance and the dock leveler falls into its operative position.
U.S. Pat. No. 3,460,175 is another example of a mechanically-operated, vertically-storing dock leveler. The illustrated dock leveler includes both a spring counterbalance and pivotable weight to assist in operation. The spring counterbalance includes a spring, cam, and cam roller. The spring counterbalance upwardly biases the dock leveler, whereas the weight downwardly biases the dock leveler when the weight is rotated into its high moment position. In operation, when the dock leveler is rotated toward the horizontal position, the weight rotates from its low moment position to its high moment position. According to the specification, when the weight is in the high moment position, the moment about the pivotal connection of the ramp to the support means is sufficient to overcome the upward biasing action of the spring so that the ramp remains in the horizontal position. To re-store the dock leveler, the weight is rotated from the high moment position to the low moment position. According to the specification, when the weight is in the low moment position, the force provided by the spring is sufficient to rotate the dock leveler into the stored, vertical position.
A drawback of the above-described dock levelers is that the spring counterbalance upwardly biases the dock leveler throughout the rotation of the dock leveler. Accordingly, rotation of the dock leveler downward is made more difficult because the motion is against the force of the spring. Another drawback of the above-described dock levelers is that they require additional components such as the arm and cam roller.
Accordingly, it is desirable to provide a spring counterbalance method and apparatus for assisting the operation of a mechanically-operated, vertically-storing dock leveler that can upwardly bias the dock leveler at certain angles of rotation, downwardly bias the dock leveler at other angles of rotation, and/or neutrally bias the dock leveler at yet other angles of rotation. It is also desirable to provide a method and apparatus for assisting the operation of a mechanically-operated, vertically-storing dock leveler of desirable simplicity.